How to talk to a Duchess

The protocol

First things first. It's easy to remember how to verbally address a duchess because you call her 'Duchess'. Good for duchesses for being so straightforward.*

If you are in a multiple-duchess situation, you say 'The Duchess of…', so everyone knows which one you mean. Including her.

If the duchess in question used to be married to a duke, you still call her 'Duchess'.

The widow of a duke - it's 'Duchess'.

A duke's mother - you guessed it. 'Duchess'. Handy.

Keep your eyes peeled for royal duchesses, though (like the Duchess of Cambridge) - you should address them as 'Your Royal Highness' on introduction, followed by 'Ma'am'. It's not a trick, it's just an exception to the rule.

* Unless you work for said duchess, in which case you should call her 'Your Grace'. This also applies when you officially announce her, as in 'Her Grace, the Duchess of Devonshire'.